3/11/11 - Practice NAB in class to include both mechanisms and Pneumatics
7/11/11 - Pneumatics Homework to be handed in
(this is in the back of your booklet and should be answered on lined paper)
- Also if you got less than 31 marks in the Mechanisms homework you need to resubmit this also
(remember to come in on Wednesday lunchtime for some extra help)
Today we looked at this circuit and answered the questions below. Again I will leave the answers as a comment so that you can attempt the questions again first before reading.
Names of Valves/components:
ReplyDelete1 - 3/2 Solenoid, Spring Return Valve
2 - 3/2 Low Pressure (not pilot!) spring return valve (diaphragm valve)
3 - Shuttle Valve
4&9 - 3/2 push button, spring return valve
5&7 - Unidirectional Flow Control Restrictor
6 - 5/2 Pilot, Pilot valve
8 - Double Acting Cylinder
10 - Single Pole, Single Throw Switch.
Function of the coloured boxes:
orange - AND control
blue - OR control (note that you can combine logic functions in pneumatics just like you can in digital electronics)
green - Air Bleed (note that the FCR is required before the air bleed to ensure that high pressure air is not released into the atmosphere as this can be very dangerous!)
Description of how the circuit works:
* Valve 1 is actuated by an electrical signal caused by closing the switch. When actuated main air flows from port 1 to port 2 and to valve 2.
* An air bleed has been created by using a Unidirectional Flow Control Restrictor to slow down main air and then a T-Piece to allow this air to escape into the atmoshpere
* Valve 2 is actuated by low pressure air caused by covering the air bleed described above.
* When both valve 1 and valve 2 are actuated air can flow through the shuttle valve (which creates OR control) and to valve 6.
* Valve 4 is also connected to the shuttle valve so when actuated sends signal air to valve 6.
* Either signal through the shuttle valve actuates valve 6 to its 1,4 state allowing main air to flow from port 1 to port 4, instroking the cylinder.
* The unidirectional Flow Control Restrictor (valve 7) restricts the exhaust of the cylinder as it instrokes, causing the cylinder to instroke slowly.
* When the push button on valve 9 is pressed this actuates it and main air can flow from port 1 to port 2 giving a signal to valve 6.
* Valve 6 is then actuated to its 1,2 state, allowing main air to flow from port 1 to port 2, outstroking the cylinder at full speed.
Calculations:
Force = Pressure x area so first the area must be calculated:
A = pi r(2)
= 3.14 x 12.5(2)
= 491mm
F = PA
= 0.3 x 491
= 147N
Area on instroke is less due to the piston rod taking up some of the effective area.
A = pi R(2) - pi r(2)
= (3.14 x 12.5(2)) - (3.14 x 2.5(2))
= 491 - 19.6
= 471.4mm
F = PA
= 0.3 x 471
= 141N